Forged-steel connecting rod blanks of the aforedescribed type can be formed in a forging die in two stages. The resulting blank is then subjected to complete mechanical machining. The most important machining step includes separation of the bearing cap from the connecting rod, followed by a machining of the separate surfaces and the subsequent provision of a bearing in the split hole or bore of the crankshaft eye which can be clamped between the bearing cap and the rod and which rotatably receives the crankshaft. The separating surface lies at the center of the crankshaft bore. In further processing steps bores are provided for the screws or bolts which draw the bearing cap against the rod, including threading where necessary, and the machining of the piston-pin bore and the crankshaft bore to the desired diameter and finish.
Such forged connecting rods must be capable of being manufactured at low cost and should be able to be carried out such that separate machining steps for the surfaces between the bearing cap and the rod are unnecessary or can be eliminated.
In EP 0 507 519 A2 a steel-forged connecting rod is described which has a crack initiating crevice which facilitates separation of the cap from the connecting rod at the crankshaft bearing eye by a breaking or cracking operation, the breakage plane lying midway of the large-diameter bore transverse to the longitudinal dimension of the rod. The break-initiating crevice or gap is a crevice which can extend parallel to the axis of the large-diameter bore and can be located along the inner wall of the crankshaft eye or the exterior of the eye. The result is the ability to crack the crankshaft bearing eye more or less cleanly. Special operating steps are, however, required to form the crevice or notch.
Another process is described in EP 0 330 830 A1 for producing connecting rods in the form of powder-forged components. It has been found, however, that here too the breakage crevice or notch must be produced in a separate working step. The intended break cracks here also extend parallel to the axis of the large-diameter bore of the connecting rod.